Compressor having a suction throttle valve

ABSTRACT

A compressor has a compression chamber formed in a cylinder block, a suction passage formed upstream of the compression chamber and a suction throttle valve formed in the suction passage for adjusting opening of the suction passage. The suction throttle valve has a valve hole and a valve seat formed around the valve hole, a valve body for opening and closing the valve hole and an urging member for urging the valve body in the direction which causes the valve hole to be closed. The urging member is a disk spring. The spring characteristics of the disk spring includes a range where the increasing rate of the load required for displacement of the disk spring is reduced with an increase of displacement of the disk spring. The displacement range of the valve body includes a range where the increasing rate of the load of the disk spring is reduced with an increase of the displacement of the disk spring.

BACKGROUND OF THE INVENTION

The present invention relates generally to a compressor, and more particularly to a compressor having a suction throttle valve in a suction passage.

A conventional piston type compressor is equipped with a stop for preventing a suction reed valve of the compressor from being vibrated by self-excitation during suction of refrigerant gas. In the piston type variable displacement compressor, however, the amount of suction gas drawn into the compressor differs between the time of maximum displacement and the time of variable displacement. When the stop is set for the maximum displacement, the suction reed valve does not open to a sufficient degree to be in contact with the stop when the displacement is small or when the displacement is minimum. As a result, the suction reed valve generates self-excited vibration to cause suction pulsation, the vibration from which may be propagated to the exterior of the compressor, thereby generating noise.

In order to solve the above problem, there has been proposed a compressor having a suction throttle valve which is adapted to control the opening area of the suction passage, thereby to reduce pressure fluctuation when the flow rate is low. Japanese Patent Application Publications No. 2000-136776 and No. 2005-337232 disclose a variable displacement compressor having an opening control valve serving as the suction throttle valve. The compressor disclosed in Japanese Patent Application Publications No. 2000-136776 has an opening control valve which is operable by a pressure difference due to the flow of refrigerant gas in the suction passage and a spring force to reduce the pressure fluctuation when flow rate is low.

Meanwhile, Japanese Patent Application Publication No. 2005-337232 discloses a variable displacement compressor having an opening control valve. The opening control valve is operable to adjust the opening of the suction passage in accordance with a pressure difference between suction pressure and pressure in the crank chamber. In the compressor, the suction pressure in a suction port acts on the opening control valve as well as the pressure in the crank chamber which varies according to the displacement. Thus, during operation of the compressor at the maximum displacement, influence of the urging force of the spring is lessened and the opening of the suction throttle valve is easily maximized. On the other hand, during the operation at a small displacement, the influence of the urging force of the spring is increased and the opening of the suction throttle valve is easily minimized.

However, in the compressor disclosed in Japanese Patent Application Publication No. 2000-136776, the opening control valve is operable from pressure difference due to the flow of refrigerant gas in the suction passage and the spring force. In this compressor, if the throttling effect by the opening control valve is given priority, the compressor operation at the maximum displacement is influenced by the throttling effect and, therefore, pressure loss is caused in the suction passage, thereby inviting a deterioration in compressing performance. If the compressing performance during the maximum displacement operation is given priority, on the other hand, sufficient throttling effect of the opening control valve is not obtained during operation at a small displacement.

The compressor of Japanese Patent Application Publication No. 2005-337232 can eliminate drawbacks of the compressor of Japanese Patent Application Publication No. 2000-136776. However, when flow rate is relatively high during operation at a variable displacement, the suction passage is subjected to the throttling effect by the opening control valve. In other words, the compressor disclosed in Japanese Patent Application Publication No. 2005-337232 can almost solve the problems of Japanese Patent Application Publications No. 2000-136776. However, despite the intention, there is another problem that a throttling effect by the opening control valve is produced in the suction passage when flow rate is relatively high during operation at a variable displacement.

The opening control valves of Japanese Patent Application Publications No. 2000-136776 and No. 2005-337232 have an urging member in the form of a compression coil spring wherein the relation between load and displacement of the spring is linear. In other words, the compression coil spring has such spring characteristics that the load required when the compression coil spring starts to be displaced is relatively small, and the load is increased in accordance with an increase of displacement of the compression coil spring. In the suction throttle valve using the compression coil spring, if a small load is required when the compression coil spring starts to be displaced, the throttling effect of the suction throttle valve is not obtained sufficiently during operation at a low refrigerant flow rate. The load of the spring is increased with an increase of the spring displacement, so that the throttling effect tends to be produced during operation at a relatively high flow rate.

The present invention, which has been made in view of the above-described problems, is directed to a compressor which ensures that the throttling effect of the suction throttle valve, which does not use crank pressure for its operation, is available during operation of the compressor at a low flow rate and also that the throttling effects of the suction throttle valve is prevented from being developed during operation of the compressor at a high flow rate.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a compressor has a compression chamber formed in a cylinder block, a suction passage formed upstream of the compression chamber and a suction throttle valve formed in the suction passage for adjusting opening of the suction passage. The suction throttle valve has a valve hole and a valve seat formed around the valve hole, a valve body for opening and closing the valve hole and an urging member for urging the valve body in the direction which causes the valve hole to be closed. The urging member is a disk spring. The spring characteristics of the disk spring includes a range where the increasing rate of the load required for displacement of the disk spring is reduced with an increase of displacement of the disk spring. The displacement range of the valve body includes a range where the increasing rate of the load of the disk spring is reduced with an increase of the displacement of the disk spring.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross sectional view of a variable displacement compressor according to the first embodiment;

FIG. 2A shows a graph showing spring characteristics of the disk spring;

FIG. 2B shows a schematic view of a disk spring as an urging member;

FIG. 3A is a partial cross sectional view of a compressor showing a suction throttle valve in its closed state during operation of the compressor at a low flow rate;

FIG. 3B is a partial cross sectional view of a compressor showing a suction throttle valve in its opened state during operation of the compressor at a high flow rate; and

FIG. 4 is a partial cross sectional view of a compressor according to a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a compressor of the first preferred embodiment according to the present invention with reference to FIGS. 1 through 3. The first preferred embodiment is an example as applied to a piston type swash plate variable displacement compressor.

The swash plate variable displacement compressor (hereinafter referred to merely as “compressor”) according to the first embodiment will now be described. In FIG. 1, the left side of the compressor on the drawing corresponds to the front side of the compressor, and the right side of the compressor on the drawing correspond to the rear side of the compressor.

As shown in FIG. 1, the compressor has a cylinder block 11. The front end of the cylinder block 11 is connected to a front housing 12 and the rear end of the cylinder block 11 is connected to a rear housing 13 through a valve plate assembly 25. The cylinder block 11 has a compression chamber 33 formed therein. The cylinder block 11 and the front housing 12 cooperate to define therein a space as a crank chamber 14.

The cylinder block 11 and the front housing 12 rotatably support a rotary shaft 15 which extends through the crank chamber 14. The front end of the rotary shaft 15 extends out of the front housing 12 and is connected to a mechanism (not shown) which receives power transmitted from a drive source (not shown) such as a vehicle engine or motor. In the crank chamber 14, a lug plate 16 is fixedly mounted on the rotary shaft 15 and a swash plate 17 which is engaged with the lug plate 16 is mounted on the rotary shaft 15.

The swash plate 17 has at its center a hole 18 through which the rotary shaft 15 is inserted through the hole 18. Guide pins 19 are provided protruding from the swash plate 17 and slidably inserted in corresponding guide holes 20 formed in the lug plate 16, whereby the swash plate 17 rotates with the rotary shaft 15 with the sliding relation of the guide pins 19 with the guide holes 20. The swash plate 17 is provided slidably in the axial direction of the rotary shaft 15 and tiltably supported by the rotary shaft 15. A thrust bearing 21 is provided in the front inner wall of the front housing 12, and the lug plate 16 is slidable relative to the front housing 12 through this thrust bearing 21.

The cylinder block 11 has formed therethrough a plurality of cylinder bores 22 arranged around the rotary shaft 15, each of which accommodates therein a piston 23 slidable in the axial direction of the rotary shaft 15. The front end of the piston 23 is engaged with the radially outer portion of the swash plate 17 through a pair of shoes 24. Therefore, the swash plate 17 rotates with the rotary shaft 15, so that the piston 23 reciprocates in the axial direction of the cylinder bore 22 through the shoes 24.

The rear housing 13 has at its center a suction chamber 26 formed therein in facing relation to the valve plate assembly 25. Similarly, the rear housing 13 has a discharge chamber 27 formed therein around the suction chamber 26. The suction chamber 26 and discharge chamber 27 are separated by a partition 13 a as shown in FIG. 1. A communication passage 28 is formed in the cylinder block 11 and the rear housing 13 for connecting the crank chamber 14 to the discharge chamber 27. An electromagnetic type displacement control valve 29 is disposed in the communication passage 28. The cylinder block 11 has a bleed passage 30 formed therein for connecting the crank chamber 14 to the suction chamber 26.

The rear housing 13 has a suction port 31 which is connected to an external refrigeration circuit (not shown). The rear housing 13 has a suction passage 32 formed therein for communicating the suction port 31 with the suction chamber 26 and located upstream of the compression chamber 33 of the cylinder block 11. The suction passage 32 has a suction throttle valve 40 formed therein for adjusting the opening of the suction passage 32. As shown FIG. 1, the suction throttle valve 40 has a valve housing 41, a valve seat 45, a valve body 48 and a disk spring 55. The valve housing 41 with a cylindrical shape is fitted in the suction passage 32. The valve seat 45 is fitted at the top end of the valve housing 41. The valve body 48 is reciprocally movably provided in the valve housing 41. The disk spring 55 as an urging means functions to urge the valve body 48 toward the valve seat 45. For the sake of description herein, in FIGS. 1 and 3, the side on the valve seat 45 of the suction throttle valve 40 will be referred to as the top side of the suction throttle valve 40 and the side on the disk spring 55 thereof as the bottom side of the suction throttle valve 40, respectively.

The valve housing 41 of the suction throttle valve 40 is made of a resin material and of a cylindrical shape with an bottom at bottom end and an opening at top end and has a valve chamber 42 whose inner diameter is constant. The bottom surface of the valve housing 41 has a hole 44 whose inner diameter is smaller than that of the valve chamber 42. The bottom surface of the valve housing 41 functions to determine the lowest position of the valve body 48. A valve hole 47 formed to be surrounded by the valve seat 45 is provided above the valve body 48.

The valve seat 45 has a flange 46 at the top portion thereof which extends horizontally outwardly. The lower surface of the flange 46 is in contact with the top surface of the valve housing 41, thus determining the vertical position of the valve seat 45 relative to the valve housing 41. The valve housing 41 has a communication port 43 formed laterally therethrough for communication with the suction passage 32. The communication port 43 of the valve housing 41 is formed in alignment with the suction passage 32 of the rear housing 13, as shown in FIG. 1. The valve body 48 is accommodated in the valve housing 41 so as to reciprocate vertically for opening and closing the valve hole 47.

The valve body 48 has a valve member 49 which faces the valve hole 47 formed therein and a rod 51 which extends downward from the bottom of the valve member 49. The outer diameter of the valve member 49 corresponds to the inner diameter of the valve housing 41 which defines the valve chamber 42. The outer diameter of the valve body 48 is set larger than that of the hole 44 at the bottom of the valve housing 41. The valve member 49 has a communication passage 50 formed therethrough which functions as a throttle in the suction passage 32 when the valve hole 47 is closed. The cross sectional area of the communication passage 50 is sufficiently smaller than that of the suction passage 32 such that a throttling effect is created between upstream and downstream of the suction throttle valve 40 in the suction passage 32.

The rod 51 provided at the bottom of the valve body 48 has at the bottom end thereof a disk plate 52 whose diameter is larger than that of the rod 51 for positive contact with the disk spring 55. The disk plate 52 has such a diameter that permits the disk plate 52 to pass through the hole 44 (or the diameter thereof is less than inner diameter of the hole 44).

The following will describe the disk spring 55 serving as an urging member for urging the valve body 48 in the direction which causes the valve hole 47 to be closed. In the first preferred embodiment, four disk springs 55 are disposed in the disk spring chamber 53 which is formed under the valve housing 41 and arranged in series in the direction in which the disk springs 55 are displaced or bent. Using a plurality of disk springs 55 provides enough displacement range or stroke range for the valve body 48.

FIG. 2A shows a graph showing the spring characteristics of the disk spring 55 and FIG. 2B shows a schematic view of the disk spring 55 in this first preferred embodiment. The disk spring 55 shown in FIG. 1 through FIG. 3 is made of metal and known in the art. As shown in FIG. 2B, the total amount of displacement h of the disk spring 55 is obtained by subtracting the thickness d from the free height H of the disk spring 55.

Referring to FIG. 2A, the solid line G1 represents the spring characteristics of the disk spring 55 and the chain double-dashed line G2 is provided for comparison with G1, showing spring characteristics of a compression coil spring whose displacement and load are proximate to those of the disk spring 55. In comparison to the compression coil spring, the spring characteristics of the disk spring 55 is set such that the load required at the beginning of the spring displacement is relatively large, and that the increasing rate of the load is decreased with an increase of the spring displacement. In the first preferred embodiment, the total displacement amount h of the disk spring 55 is not used for the displacement range of the valve body 48, but part of the total displacement h of the disk spring 55 corresponds to the displacement range of the valve body 48. It can be said that the displacement range of the valve body 48 includes a range where the increasing rate of the load of the disk spring 55 decreases with an increase of the displacement amount of the disk spring 55. A range where the disk spring 55 does not reverse corresponds to the displacement range of the valve body 48, which prevents the disk spring 55 from reversing during operation at the maximum displacement.

The total displacement h of the disk spring 55 is set 1.4 times as large as the thickness of the disk spring 55 in the first preferred embodiment. This value makes it possible for the spring characteristics to include a range where the increasing rate of the load required for displacement of the disk spring 55 is reduced with an increase of displacement of the disk spring 55. The relation between the load and the displacement of the compression coil spring is substantially linear and this differs from the characteristics of the disk spring 55 in that the spring characteristics of the disk spring 55 includes a range where the increasing rate of the load required for displacement is reduced with an increase of the displacement. This is because the disk spring 55 has a nonlinear spring constant.

Referring to FIG. 2A, the load of the disk spring 55 is larger than that of the compression coil spring in the initial stage of displacement, but it is smaller than that of the compression coil spring at the maximum displacement. The displacement range of the valve body 48 includes a range where the increasing rate of the load is reduced with an increase of the displacement. With the suction throttle valve 40 closed where the displacement range of the valve body 48 is zero, urging force of the disk spring 55 is present, and presses the valve body 48 against the valve seat 45 with the valve hole 47 closed by the valve body 48. The upper limit of the displacement range of the valve body 48 is set such that the disk spring 55 will not be reversed when the valve is fully opened.

The relation of the displacement between the disk spring 55 and the valve body 48 is such that the valve hole 47 continues to be closed unless the load of the valve body 48 due to the suction pressure becomes greater than the urging force of the disk spring 55. Meanwhile, after the load of the valve body 48 under the suction pressure exceed the urging force of the disk spring 55, a slight increase of the load maximizes the displacement of the valve body 48, thereby opening the valve hole 47.

The following describes the operation of the compressor of the first preferred embodiment.

In accordance with the reciprocating movement of the piston 23 due to the rotation of the rotary shaft 15, refrigerant gas in the suction chamber 26 is introduced through a suction hole into the cylinder bore 22 with the suction valve opened. The refrigerant gas in the cylinder bore 22 is compressed and then discharged through a discharge hole in the valve plate assembly 25 into the discharge chamber 27 with the discharge valve opened. Subsequently, most of the high-pressure refrigerant gas discharged into the discharge chamber 27 is delivered to the external refrigeration circuit (not shown).

The relation between the amount of refrigerant gas introduced from the discharge chamber 27 through the communication passage 28 into the crank chamber 14 and the amount of refrigerant gas flowing out from the crank chamber 14 through the bleed passage 30 into the suction chamber 26 is controlled by changing the opening of the displacement control valve 29, thereby determining the crank pressure Pc in the crank chamber 14.

Varying the crank pressure Pc in the crank chamber 14 by changing the opening of the displacement control valve 29, the pressure difference between the crank chamber 14 and the cylinder bore 22 through the piston 23 is changed and the inclination angle of the swash plate 17 is changed, accordingly. The stroke of the piston 23 is varied by changing the inclination angle of the swash plate 17 and the displacement of the compressor is changed in accordance with the change of the stroke of the piston 23.

When the crank pressure Pc is reduced, the inclination angle of the swash plate 17 is increased, so that the stroke of the piston 23 is increased and the displacement of the compressor is increased, accordingly. Meanwhile, when the crank pressure Pc is increased, the inclination angle of the swash plate 17 is reduced, so that the stroke of the piston is reduced and the displacement of the compressor is decreased, accordingly.

The displacement of the compressor is determined by the inclination angle of the swash plate 17 which corresponds to the opening of the displacement control valve 29. For example, in the process of changing the displacement control valve 29 to open from its closed state, the inclination angle of the swash plate 17 becomes gradually smaller and the displacement is changed, accordingly. Thus, the compressor operates at an intermediate displacement between the maximum and minimum displacements. When the inclination angle of the swash plate 17 becomes minimum, the compressor operates in its minimum. During the minimum displacement operation when the pressure of the suction passage 32 is reduced to a low level, the load acting on the valve body 48 due to the pressure of the suction passage 32 is smaller than the urging force of the disk spring 55.

The valve body 48 receiving such urging force of the disk spring 55 is located at its uppermost position and, therefore, the valve hole 47 is closed. Although the valve hole 47 is closed, upstream and downstream of the suction throttle valve 40 in the suction passages 32 is in communication with each other through the communication passage 50. Therefore, the communication passage 50 functions as a throttle providing a throttling effect in the suction passage 32. In other words, throttling effect is generated in the suction passage 32 by closing the valve hole 47, so that the pressure fluctuation in the suction passage 32 is prevented and the propagation of the suction pulsation due to the self-excited vibration of the suction valve is also prevented.

When the compressor is operating at a low speed at an intermediate displacement between the maximum and minimum displacements, the flow rate remains low and the pressure in the suction passage 32 or the load acting on the valve body 48 remains smaller than the urging force of the disk spring 55. Thus, the valve hole 47 is kept closed by the valve body 48, so that propagation of the suction pulsation due to the self-excited vibration of the suction valve is prevented by the throttling effect of the communication passage 50.

On the other hand, when the compressor is operated at a high speed at an intermediate displacement between the maximum and minimum displacements and the flow rate is so large that the load on the valve body 48 due to the pressure of the suction passage 32 is beyond the urging force of the disk spring 55, the valve body 48 moves away from the valve seat 45 in accordance with the pressure in the suction passage 32. Although the load required to cause the disk spring 55 to start its displacement is set relatively large, the difference between this load for starting the displacement of the disk spring 55 and the load required for maximum displacement of the disk spring 55 is relatively small. Thus, the throttling effect by the valve body 48 is alleviated and the pressure loss in the suction passage 32 due to the valve body 48 is prevented.

In the process of changing of the displacement control valve 29 from the opened state to the closed state, the inclination angle of the swash plate 17 becomes gradually larger and, finally, the compressor is operated at the maximum displacement. Because the pressure in the suction passage 32 during this maximum-displacement operation is larger than during operation at an intermediate displacement between the maximum and minimum displacements, the valve body 48 remains at the lowermost position. Thus, the throttling effect due to the valve body 48 is alleviated in the suction passage 32 and the refrigerant gas is introduced from the suction chamber 26 into the cylinder bore 22 at a rate corresponding to the maximum displacement.

The compressor of the present embodiment has the following advantageous effects.

(1) In the compressor with the suction throttle valve 40 which does not utilize the pressure in the crank chamber, the throttling effect by the suction throttle valve 40 is certainly created during the operation at a low flow rate. Additionally, the throttling effect due to the suction throttle valve 40 is certainly prevented during the operation at a high flow rate.

(2) The disk spring 55 is set such that its spring characteristics include a range where the increasing rate of the load required for displacement is decreased with an increase of displacement of the disk spring 55, and also that the displacement range of the valve body 48 includes a range of the spring characteristics where the increasing rate of the load required for displacement with the increase of the displacement of the disk spring 55 is decreased. Thus, the difference between the load which is necessary for the valve body 48 to move to its maximum displacement position thereby to displace the disk spring 55 to an extent that is close to the maximum displacement and the load of the disk spring 55 at which the disk spring 55 begins to be displaced is set relatively small. Accordingly, the valve body 48 is moved thereby to close the valve hole 47 by a slight pressure fluctuation during operation under a relatively low suction pressure and hence at a low flow rate. Meanwhile, the valve hole 47 can remain open without being influenced by a little pressure fluctuation during operation under a relatively high suction pressure and hence at a high flow rate.

(3) Because a plurality of disk springs 55 are disposed in series in the direction in which the disk spring 55 is displaced, the stroke of the valve body 48 can be increased while maintaining the spring characteristics of the disk spring 55. Additionally, the use of disk spring 55 as an urging member is advantageous in that urging force to the valve body 48 can be applied easily and also that the space required for installation in a limited space of a compressor may be reduced.

(4) The total displacement h of the disk spring 55 is set 1.4 times as large as the thickness of the disk spring 55, so that the spring characteristics can include a range where the increasing rate of the load required for displacement of the disk spring 55 is decreased with an increase of displacement of the disk spring 55. Thus, the urging member which is suitable for opening/closing condition of the valve body 48 of the suction throttle valve 40 can be provided.

(5) As compared to a compressor with a suction throttle valve using pressure in the crank chamber, the compressor of the above-described embodiment can dispense with a communication passage for allowing the pressure in the crank chamber to be transmitted the suction throttle valve 40 and, therefore, the compressor is simplified.

The following will describe a compressor of the second preferred embodiment according to the present invention with reference to FIG. 4 which is a partially enlarged fragmentary cross sectional view showing the compressor of the second embodiment.

For convenience of explanation, common or similar elements or parts are designated by the same reference numerals as those used in the first preferred embodiment and, therefore, the description of such similar elements or parts will be omitted and only the modifications will be described.

As shown in FIG. 4, the compressor of the second embodiment has a suction throttle valve 60. The suction throttle valve 60 has a valve housing 61 including a valve chamber 62 and a communication port 63, a valve seat 65 including a flange 66 and a valve hole 67, a valve body 68 including a valve member 69 and a communication passage 70 and a plurality of disk springs 75. The valve housing 61 of the second preferred embodiment differs from the valve housing 41 of the first preferred embodiment in that the valve housing 61 has a cylindrical shape with an opening at both ends. The valve member 69 of the valve body 68 has a contact portion 71 formed at the bottom thereof which is in contact with the disk spring 75.

The contact portion 71 of the valve body 68 has a guide rod 72 extending downwardly from the bottom thereof. A hole is formed to be surrounded by the disk spring 75. The guide rod 72 whose diameter is smaller than that of a hole of the disk spring 75 and inserted through the holes of all disk springs 75. Thus, the uppermost disk spring 75 is located closer to the valve member 69 than in the first preferred embodiment. The suction throttle valve 60 has a disk spring chamber 73 below the valve body 68 and a rod hole 74 is formed extending downwardly from the disk spring chamber 73 in which the guide rod 72 is inserted. The guide rod 72 is inserted through the holes of all disk springs 75, thereby functioning as a guide for the disk spring 75 in displacing, and also regulating the irregular movement of the disk spring 75 in the horizontal direction. In addition, the disk spring 75 has the same structure as the disk spring 55 of the first preferred embodiment and the same spring characteristics as shown in FIG. 2A.

The second preferred embodiment offers not only the same advantageous effects as the first preferred embodiment, but also the following advantages.

The guide rod 72 of the valve body 68 functions as a guide and regulates the irregular movement of the disk spring 75 in the horizontal direction, thereby preventing unstable reciprocation of the valve body 68 due to the irregular movement of the disk spring 75.

In addition, the contact portion 71 of the valve body 68 has a guide rod 72 and the disk spring 75 is located close to the valve member 69, so that the volume of the valve chamber 62 is made smaller than that of the valve chamber 42 of the first preferred embodiment, with the result that the suction throttle valve 60 can be downsized.

The present invention is not limited to the above-described embodiments but may be modified into alternative embodiments as exemplified below.

Although a plurality of disk springs is used as an urging member in the first and second preferred embodiments, the number of the disk springs is not limited. One or more disk springs may be provided and the number and size of the disk springs may be determined according to the required displacement of the valve body.

Although the communication passage for throttling is provided above the valve member of the valve body in the first and second preferred embodiments, the communication passage is not limited to such arrangement. For example, a communication passage may be provided which directly connects the suction passage of upstream side to the suction chamber, so that the valve body fully closes the valve hole. In this case, when the valve body fully closes the valve hole, the throttling effect is produced by the communication passage connecting the suction passage of upstream side to the suction chamber.

In the first and second preferred embodiments, the total displacement of the disk spring is set 1.4 times as large as the thickness of the disk spring, but it is not limited to the 1.4 times. For obtaining spring characteristics which includes a range where the increasing rate of the load required for displacement of the disk spring is decreased with an increase of displacement of the disk spring, the above value for ratio is to be 1.4 or greater for practical application. What is important is that the value for ratio is not to be set less than 1.4.

In the first and second preferred embodiments, the load required for the disk spring to start to be displaced is set relatively larger than that of the compression coil spring. Additionally, the spring is set for such characteristics that they include a range where the increasing rate of the load for displacement of the disk spring is decreased with an increase of displacement of the disk spring. However the spring is not limited to the above characteristics. The initial urging force of the disk spring may be set in such a way that the load of the disk spring is decreased with an increase of the displacement of the disk spring due to the displacement of the valve body. The initial urging force is the force of the disk spring that urges the valve body against the valve seat when the valve body is seated on the valve seat.

In this case, when the load acting on the valve body just exceeds the initial load of the disk spring, the load of the disk spring is reduced. That is, when the load acting on the valve body just exceeds the initial load, the valve body is moved to the maximum displacement position. In this case, the valve hole of the suction throttle valve is closed by the valve body during operation at a low flow rate when the suction pressure is low and fully opened during operation at a high flow rate when the suction pressure is high.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims. 

1. A compressor comprising: a compression chamber formed in a cylinder block; a suction passage formed upstream of the compression chamber; and a suction throttle valve formed in the suction passage for adjusting opening of the suction passage, wherein the suction throttle valve has a valve hole and a valve seat formed around the valve hole, a valve body for opening and closing the valve hole and an urging member for urging the valve body in the direction which causes the valve hole to be closed, wherein the urging member is a disk spring, wherein the spring characteristics of the disk spring includes a range where the increasing rate of the load required for displacement of the disk spring is reduced with an increase of displacement of the disk spring, and wherein the displacement range of the valve body includes a range where the increasing rate of the load of the disk spring is reduced with an increase of the displacement of the disk spring.
 2. The compressor according to claim 1, wherein the urging member is a plurality of disk springs arranged in series in the direction in which the disk springs are displaced.
 3. The compressor according to claim 1, the total displacement of the disk spring is set 1.4 times or greater as large as the thickness of the disk spring.
 4. The compressor according to claim 1, wherein where the valve hole is kept closed by the valve body, the initial urging force of the disk spring is set in such a way that the load of the disk spring is decreased with an increase of the displacement of the disk spring due to the displacement of the valve body.
 5. The compressor according to claim 1, wherein the valve body has a guide rod extending downwardly from the bottom thereof and the guide rod is inserted through a rod hole of the disk spring.
 6. The compressor according to the claim 1, wherein a communication passage is formed through the valve body, and upstream and downstream of the suction throttle valve in the communication passage is in communication with each other through the communication passage when the valve hole is closed. 